Carbon blacks are generally produced in a furnace-type reactor by pyrolyzing a hydrocarbon feedstock with hot combustion gases to produce combustion products containing particulate carbon black.
In one type of a furnace carbon black reactor, such as shown in U.S. Pat. No. 3,401,020 to Kester et al., or U.S. Pat. No. 2,785,964 to Pollock, hereinafter "Kester" and "Pollock" respectively, a fuel, preferably hydrocarbonaceous, and an oxidant, preferably air, are injected into a first zone and react to form hot combustion gases. A hydrocarbon feedstock in either gaseous, vapor or liquid form is also injected into the first zone whereupon pyrolysis of the hydrocarbon feedstock commences. In this instance, pyrolysis refers to the thermal decomposition of a hydrocarbon. The resulting combustion gas mixture, in which pyrolysis is occurring, then passes into a reaction zone where completion of the carbon black forming reaction occurs.
In another type of a furnace carbon black reactor, a liquid or gaseous fuel is reacted with an oxidant, preferably air, in the first zone to form hot combustion gases. These hot combustion gases pass from the first zone, downstream through the reactor, into a reaction zone and beyond. To produce carbon blacks, a hydrocarbonaceous feedstock is injected at one or more points into the path of the hot combustion gas stream. The hydrocarbonaceous feedstock may be liquid, gas or vapor, and may be the same or different than the fuel utilized to form the combustion gas stream. The first (or combustion) zone and the reaction zone may be divided by a choke or zone of restricted diameter which is smaller in cross section than the combustion zone or the reaction zone. The feedstock may be injected into the path of the hot combustion gases upstream of, downstream of, and/or in the restricted diameter zone. Furnace carbon black reactors of this type are generally described in U.S. Pat. Reissue No. 28,974 and U.S. Pat. No. 3,922,335.
Although two types of furnace carbon black reactors and processes have been described, it should be understood that the present invention can be used in any other furnace carbon black reactor or process in which carbon black is produced by pyrolysis and/or incomplete combustion of hydrocarbons.
In both types of processes and reactors described above, and in other generally known reactors and processes, the hot combustion gases are at a temperature sufficient to effect pyrolysis of the hydrocarbonaceous feedstock injected into the combustion gas stream. In one type of reactor, such as disclosed in Kester, feedstock is injected, at one or more points, into the same zone where combustion gases are being formed. In other type reactors or processes the injection of the feedstock occurs, at one or more points, after the combustion gas stream has been formed. In either type of reactor, since the hot combustion gas stream is continually flowing downstream through the reactor, pyrolysis continually occurs as the mixture of feedstock and combustion gases passes through the reaction zone. The mixture of feedstock and combustion gases in which pyrolysis is occurring is hereinafter referred to, throughout the application, as "the effluent". The residence time of the effluent in the reaction zone of the reactor is sufficient, and under conditions suitable, to allow the formation of carbon blacks. "Residence time" refers to the amount of time which has elapsed since the initial contact between the hot combustion gases and the feedstock. After carbon blacks having the desired properties are formed, the temperature of the effluent is further lowered to stop pyrolysis. This lowering of the temperature of the effluent to stop pyrolysis may be accomplished by any known manner, such as by injecting a quenching fluid, through a quench, into the effluent. As generally known to those of ordinary skill in the art, pyrolysis is stopped when the desired carbon black products have been produced in the reactor. One way of determining when pyrolysis should be stopped is by sampling the effluent and measuring its toluene extract level. Toluene extract level is measured by ASTM D1618-83 "Carbon Black Extractables--Toluene Discoloration". The quench is generally located at the point where the toluene extract level of the effluent reaches an acceptable level for the desired carbon black product being produced in the reactor. After pyrolysis is stopped, the effluent generally passes through a bag filter system to separate and collect the carbon blacks.
Generally a single quench is utilized. Kester, however, discloses the use of two quenches to control certain properties of carbon blacks. Kester relates to controlling the modulus-imparting properties of carbon blacks by heat treatment. This heat treatment is achieved by regulating the water flow rates to two water spray quenches, positioned in series, in the effluent smoke in a carbon black furnace. The modulus of a carbon black relates to the performance of the carbon black in a rubber product. As explained in the article by Schaeffer and Smith, "Effect of Heat Treatment on Reinforcing Properties of Carbon Black" (Industrial and Engineering Chemistry, Vol. 47, No. 6; Jun. 1955, page 1286), hereinafter "Schaeffer", it is generally known that heat treatment will effect the modulus-imparting properties of carbon black. However, as further explained in Schaeffer, the change in the modulus-imparting properties of carbon blacks produced by heat treating results from a change in the surface chemistry of the carbon blacks. Therefore, positioning the quenches as suggested by Kester, in order to subject the combustion gas stream to different temperature conditions, affects the modulus-imparting properties of carbon black apparently by changing the surface chemistry of the carbon blacks rather than by affecting the morphology of the carbon blacks in any discernible way. Moreover, in Kester, both quenches are located in a position in the reaction zone where significant pyrolysis of the feedstock has already occurred. Thus, it would appear that, in Kester's process, by the time the effluent reaches the first quench, the CTAB, tint, DBP and Stokes diameter properties of the carbon blacks have been defined. This supports the conclusion that the change in the modulus-imparting properties in Kester does not result from a change in the morphological properties of the carbon blacks. Still further, Kester does not attach any significance to the position of the first quench, relative to the point of injection of feedstock or residence time, and does not disclose means for selecting the position of the first quench.
U.S. Pat. No. 4,230,670 to Forseth, hereinafter "Forseth", suggests the use of two quenches to stop pyrolysis. The two quenches are located inches apart at the point where a single quench would be located. The purpose of the two quenches is to more completely fill the reaction zone with quenching fluid to more effectively stop pyrolysis. In Forseth however, by the time the effluent reaches the quenches, the CTAB, Tint, DBP and Stokes Diameter properties of the carbon blacks have been defined.
U.S. Pat. No. 4,265,870, to Mills et al., and U.S. Pat. No. 4,316,876, to Mills et al., suggest using a second quench located downstream of the first quench to prevent damage to the filter system. In both patents the first quench completely stops pyrolysis and is located at a position generally known to the art, and by the time the effluent reaches the first quench, the CTAB, Tint, DBP and Stokes Diameter properties of the carbon blacks have been defined. The second quench further reduces the temperature of the combustion gas stream to protect the filter unit.
U.S. Pat. No. 4,358,289, to Austin, hereinafter "Austin", also relates to preventing damage to the filter system by the use of a heat exchanger after the quench. In this patent also, the quench completely stops pyrolysis and is located at a position generally known to the art. In Austin, by the time the effluent reaches the first quench, the CTAB, tint, DBP and Stokes diameter properties of the carbon blacks have been defined.
U.S. Pat. No. 3,615,211 to Lewis, hereinafter "Lewis", relates to a method for improving the uniformity of carbon blacks produced by a reactor, and for extending the life of a reactor. To improve uniformity and extend reactor life, Lewis suggests using a plurality of quenches, located throughout the reaction zone, to maintain a substantially constant temperature in the reaction zone. A certain quantity of quenching fluid is injected at the quench located furthest upstream in the reactor, with a greater amount of quenching fluid injected at each subsequent downstream quench. The quench located furthest downstream stops pyrolysis. By maintaining a constant temperature in the reaction zone the apparatus of Lewis promotes uniformity in the carbon blacks produced by the apparatus. However, the plurality of quenches does not control the morphology of carbon blacks produced by the apparatus.
It is generally desirable, however, to be able to control the morphology of carbon blacks such that carbon blacks well suited to a particular end use may be produced. It is also desirable to increase the aggregate size and structure of carbon blacks for a given surface area, since increased aggregate size and structure, as represented by higher DBP, lower tint, and larger Stokes Diameter, makes the carbon blacks better suited for certain end uses.
Accordingly an object of the present invention is to provide a method for controlling the aggregate size and structure of carbon blacks.
An additional object of the present invention is to produce carbon blacks having larger aggregate size and higher structure for a given surface area.